Publications
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Articles in scientific journals
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Books
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Theses
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1. Articles in scientific journals
| Flexoelectric fluid membrane vesicles in spherical confinement
Niloufar Abtahi, Lila Bouzar, Nadia Saidi-Amroun, Martin Michael Müller | EPL, 131(1): 18001, 2020. See also arXiv:2006.04475.
| Isometric bending requires local constraints on free edges
Jemal Guven, Martin Michael Müller, Pablo Vázquez-Montejo | Math. Mech. Solids, 24: 4051, 2019. See also arXiv:1904.05855.
| Helical Superstructure of Intermediate Filaments
Lila Bouzar, Martin Michael Müller, René Messina, Bernd Nöding, Sarah Köster, Hervé Mohrbach, Igor M. Kulić |
Intermediate filaments are the least explored among the large cytoskeletal elements.
We show here that they display conformational anomalies in narrow microfluidic channels.
Their unusual behavior can be understood as the consequence of a previously undetected, large scale
helically curved superstructure. Confinement in a channel orders the otherwise soft, strongly
fluctuating helical filaments and enhances their structural correlations, giving rise to experimentally
detectable, strongly oscillating tangent correlation functions. We propose an explanation for the detected
intrinsic curving phenomenon - an elastic shape instability that we call autocoiling. The mechanism
involves self-induced filament buckling via a surface stress located at the outside of the
cross-section. The results agree with ultrastructural findings and rationalize for the commonly observed
looped intermediate filament shapes. Beyond curvature, explaining the molecular origin of the detected helical
torsion remains an interesting challenge.
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Phys. Rev. Lett., 122: 098101, 2019. See also arXiv:1803.04691.
| Vesicle dynamics in confined steady and harmonically modulated Poiseuille flows
Zakaria Boujja, Chaouqi Misbah, Hamid Ez-Zahraouy, Abdelilah Benyoussef, Thomas John, Christian Wagner, Martin Michael Müller |
We present a numerical study of the time-dependent motion of a membrane vesicle in a
channel under an imposed flow. In a Poiseuille flow the shape of the vesicle depends on the flow strength,
the mechanical properties of the membrane, and the width of the channel. In a wide parameter region, the
emerging snaking shape shows an oscillatory motion like a swimmer flagella even though the flow is
stationary. We quantify this behavior by the amplitude and frequency of the oscillations of the vesicle's
center of mass. The influence of an amplitude modulation of the imposed flow on the dynamics and shape of
the snaking vesicle is also investigated. We find that this modulation---when sufficiently small---induces
a modulation in amplitude and frequency of the center of mass of the snaking vesicle. For large
modulation amplitudes transitions to static shapes are observed.
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Phys. Rev. E, 98: 043111, 2018. See also arXiv:1810.04500.
| Confining a fluid membrane vesicle of toroidal topology in an adhesive hard sphere
Lila Bouzar, Ferhat Menas, Martin Michael Müller |
Abstract
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IOP Conf. Series: MSE, 186: 012021, 2017.
| Squeezed helical elastica
Lila Bouzar, Martin Michael Müller, Pierre Gosselin, Igor M. Kulić, Hervé Mohrbach |
We theoretically study the conformations of a helical semi-flexible filament
confined to a two-dimensional surface. This squeezed helix exhibits a variety of unexpected shapes
resembling circles, waves or spirals depending on the material parameters. We explore the conformation
space in detail and show that the shapes can be understood as the mutual elastic interaction of
conformational quasi-particles. Our theoretical results are potentially useful to
determine the material parameters of such helical filaments in an experimental setting.
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Eur. Phys. J. E, 39: 114, 2016. See also arXiv:1606.03611.
| How bio-filaments twist membranes
Julien Fierling, Albert Johner, Igor M. Kulić, Hervé Mohrbach, Martin Michael Müller |
Abstract
Soft Matter, 12: 5747, 2016.
| Toroidal membrane vesicles in spherical confinement
Lila Bouzar, Ferhat Menas, Martin Michael Müller |
We investigate the morphology of a toroidal fluid membrane vesicle confined inside a spherical container.
The equilibrium shapes are assembled in a geometrical phase diagram as a function of scaled area and
reduced volume of the membrane. For small area the vesicle can adopt its free form. When increasing
the area, the membrane cannot avoid contact and touches the confining sphere along a circular contact line,
which extends to a zone of contact for higher area. The elastic energies of the equilibrium shapes are
compared to those of their confined counterparts of spherical topology to predict under which conditions a
topology change is favored energetically.
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Phys. Rev. E, 92: 032721, 2015. See also arXiv:1509.00765.
| Non-linear buckling and symmetry breaking of a soft elastic sheet sliding on a cylindrical substrate
Norbert Stoop, Martin Michael Müller |
Abstract
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Int. J. Non-Linear Mech., 75: 115, 2015. See also arXiv:1503.05030.
| Crunching Biofilament Rings
Julien Fierling, Martin Michael Müller, Hervé Mohrbach, Albert Johner, Igor M. Kulić |
Abstract
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Europhys. Lett., 107(6): 68002, 2014. See also arXiv:1408.6787.
| Confotronic dynamics of tubular filaments
Osman Kahraman, Hervé Mohrbach, Martin Michael Müller, Igor M. Kulić |
Abstract
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Soft Matter, 10(16): pp. 2836-2847, 2014. See also arXiv:1312.3106.
| Whirling skirts and rotating cones
Jemal Guven, J. A. Hanna, Martin Michael Müller |
Abstract
New J. Phys., 15: 113055, 2013. See also arXiv:1306.2619.
| Myotubularin and PtdIns3P remodel the sarcoplasmic reticulum in muscle in vivo
Leonela Amoasii, Karim Hnia, Gaëtan Chicanne, Andreas Brech, Belinda Simone Cowling, Martin Michael Müller, Yannick Schwab, Pascale Koebel, Arnaud Ferry, Bernard Payrastre, Jocelyn Laporte |
The sarcoplasmic reticulum (SR) is a specialized form of endoplasmic reticulum (ER) in skeletal muscle
and is essential for calcium homeostasis. The mechanisms involved in SR
remodeling and maintenance of SR subdomains are elusive. In this study, we identified
myotubularin (MTM1), a phosphatase mutated in X-linked centronuclear myopathy
(XLCNM), as a key regulator of phosphoinositide-3-monophosphate (PtdIns3P) levels at the
SR. Mtm1 deficient mouse muscles and myoblasts from XLCNM patients exhibit abnormal
SR/ER networks. In vivo modulation of MTM1 enzymatic activity in muscle using ectopic
expression of wild-type or a dead-phosphatase MTM1 protein leads to differential SR
remodeling. Active MTM1 is associated to flat membrane stacks, while dead-phosphatase
MTM1 mutant promotes highly curved cubic membranes originating from the SR and
enriched in PtdIns3P. Moreover, expression of the PtdIns3P binding module 2XFYVE also
modified the SR shape at triads. Our findings, supported by the parallel analysis of the Mtm1-
null mouse and in vivo study, reveal a direct function of MTM1 enzymatic activity in SR
remodeling and a key role for its substrate PtdIns3P in promoting SR membrane curvature in
skeletal muscle. We propose that alteration in SR remodeling is a primary cause of X-linked
centronuclear myopathy. The tight regulation of PtdIns3P on specific membrane subdomains
may be a general mechanism to control membrane curvature.
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J. Cell Sci., 126(8): 1806, 2013.
| Dipoles in thin sheets
Jemal Guven, J. A. Hanna, Osman Kahraman, Martin Michael Müller |
Abstract
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Eur. Phys. J. E, 36: 106, 2013. See also arXiv:1212.3262.
| Fluid membrane vesicles in confinement
Osman Kahraman, Norbert Stoop, Martin Michael Müller |
Abstract
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New J. Phys., 14: 095021, 2012.
| Petal shapes of sympetaleous flowers: the interplay between growth, geometry and elasticity
Martine Ben Amar, Martin Michael Müller, Miguel Trejo |
The growth of a thin elastic sheet imposes constraints on its geometry such as its Gaussian curvature KG.
In this paper, we construct the shapes of sympetalous bell-shaped flowers with a constant Gaussian curvature. Minimizing the bending energies
of both the petal and the veins, we are able to predict quantitatively the global shape of these flowers. We discuss two toy problems
where the Gaussian curvature is either negative or positive. In the former case the axisymmetric pseudosphere turns out to mimic the correct
shape before edge curling; in the latter case, singularities of the mathematical surface coincide with strong veins. Using a variational
minimization of the elastic energy, we find that the optimal number for the veins is either four, five or six, a number which is deceptively
close to the statistics on real flowers in nature.
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New J. Phys., 14: 085014, 2012. Also featured in the Highlights of 2012.
| Morphogenesis of membrane invaginations in spherical confinement
Osman Kahraman, Norbert Stoop, Martin Michael Müller |
Abstract
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Europhys. Lett., 97(6): 68008, 2012. See also arXiv:1201.2518.
| Conical instabilities on paper
Jemal Guven, Martin Michael Müller, Pablo Vázquez-Montejo |
The stability of the fundamental defects of an unstretchable flat sheet is examined.
This involves expanding the bending energy to second order in deformations about the
defect. The modes of deformation occur as eigenstates of a fourth-order linear differential
operator. Unstretchability places a global linear constraint on these modes. Conical
defects with a surplus angle exhibit an infinite number of states. If this angle is below a
critical value, these states possess an n-fold symmetry labeled by an integer, n ≥ 2. A
nonlinear stability analysis shows that the 2-fold ground state is stable, whereas excited
states possess 2(n - 2) unstable modes which come in even and odd pairs.
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J. Phys. A: Math. Theor., 45(1): 015203, 2012. See also arXiv:1107.5008.
| Interface-mediated interactions: Entropic forces of curved membranes
Pierre Gosselin, Hervé Mohrbach, Martin Michael Müller |
Particles embedded in a fluctuating interface experience forces and torques
mediated by the deformations and by the thermal fluctuations of the medium.
Considering a system of two cylinders bound to a fluid membrane we show that
the entropic contribution enhances the curvature-mediated repulsion between
the two cylinders. This is contrary to the usual attractive Casimir force in
the absence of curvature-mediated interactions. For a large distance between
the cylinders, we retrieve the renormalization of the surface tension of a
flat membrane due to thermal fluctuations.
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Phys. Rev. E, 83(5): 051921, 2011. See also arXiv:1011.1221.
| Self-Contact and Instabilities in the Anisotropic Growth of Elastic Membranes
Norbert Stoop, Falk K. Wittel, Martine Ben Amar, Martin Michael Müller, Hans J. Herrmann |
Abstract
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Phys. Rev. Lett., 105(6): 068101, 2010. See also arXiv:1007.1871.
| Cell Model Approach to Membrane Mediated Protein Interactions
Martin Michael Müller, Markus Deserno |
Membrane-deforming proteins can interact through the curvature
fields they create. In the case of many such proteins a cell model
approach can be used to calculate the energy per protein and
predict, whether it would lead to phase segregation or
bud-formation. Using covariant differential geometry exact results
are derived for the lateral pressure in terms of geometric
properties at the cell boundary. Numerical solutions of the exact
shape equations in the highly nonlinear regime are found and it is
seen that both phase segregation and bud formation can occur.
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Prog. Theor. Phys. Suppl., 184: pp. 351-363, 2010.
| Hamiltonian formulation of surfaces with constant Gaussian curvature
Miguel Trejo, Martine Ben Amar, Martin Michael Müller |
Dirac's method for constrained Hamiltonian systems is used to describe surfaces of constant Gaussian curvature. A geometrical free energy, for which these surfaces are equilibrium states, is introduced and interpreted as an action. An equilibrium surface can then be generated by the evolution of a closed space curve.
Since the underlying action depends on second derivatives, the velocity of the curve and its conjugate momentum must be included in the set of phase space variables. Furthermore, the action is linear in the acceleration of the curve and possesses a local symmetry---reparametrization invariance---which implies primary constraints in the canonical formalism. These constraints are incorporated into the Hamiltonian through Lagrange multiplier functions, that are identified as the components of the acceleration of the curve. The formulation leads to four first order partial differential equations, one for each canonical variable.
With the appropriate choice of parametrization only one of these equations has to be solved to obtain the surface which is swept out by the evolving space curve. To illustrate the formalism, several evolutions of pseudospherical surfaces are discussed.
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J. Phys. A: Math. Theor., 42(42): 425204, 2009.
| Local Membrane Mechanics of Pore-Spanning Bilayers
Ingo Mey, Milena Stephan, Eva K. Schmitt, Martin Michael Müller, Martine Ben Amar, Claudia Steinem, Andreas Janshoff |
Abstract
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J. Am. Chem. Soc., 131(20): pp. 7031-7039, 2009.
| Elasticity Mapping of Pore-Suspending Native Cell Membranes
Bärbel Lorenz, Ingo Mey, Siegfried Steltenkamp, Tamir Fine, Christina Rommel, Martin Michael Müller, Alexander Maiwald, Joachim Wegener, Claudia Steinem, Andreas Janshoff |
Abstract
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Small, 5(7): pp. 832-838, 2009.
| Conical Defects in Growing Sheets
Martin Michael Müller, Martine Ben Amar, Jemal Guven |
Abstract
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Phys. Rev. Lett., 101(15): 156104, 2008. See also arXiv:0807.1814.
| How paper folds: bending with local constraints
Jemal Guven, Martin Michael Müller |
Abstract
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J. Phys. A: Math. Theor., 41(5): 055203, 2008. See also arXiv:0712.0978.
| Contact lines for fluid surface adhesion
Markus Deserno, Martin Michael Müller, Jemal Guven |
Abstract
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Phys. Rev. E, 76(1): 011605, 2007. See also cond-mat/0703019. Also featured in the Virtual Journal of Biological Physics Research.
| Balancing torques in membrane-mediated interactions: Exact results and
numerical illustrations
Martin Michael Müller, Markus Deserno, Jemal Guven |
Torques on interfaces can be described by a divergence-free tensor
which is fully encoded in the geometry. This tensor consists of two
terms, one originating in the couple of the stress, the other capturing
an intrinsic contribution due to curvature. In analogy to the description
of forces in terms of a stress tensor, the torque on a particle can be
expressed as a line integral along any contour surrounding the particle.
Interactions between particles mediated by a fluid membrane are studied
within this framework. In particular, torque balance places a strong
constraint on the shape of the membrane. Symmetric two-particle
configurations admit simple analytical expressions which are valid
in the fully nonlinear regime; in particular, the problem may be
solved exactly in the case of two membrane-bound parallel cylinders.
This apparently simple system provides some flavor of the remarkably
subtle nonlinear behavior associated with membrane-mediated interactions.
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Phys. Rev. E, 76(1): 011921, 2007. See also cond-mat/0702340. Also featured in the Virtual Journal of Biological Physics Research.
| Aggregation and vesiculation of membrane proteins by curvature-mediated
interactions
Benedict J. Reynwar, Gregoria Illya, Vagelis A. Harmandaris, Martin Michael Müller, Kurt Kremer, Markus Deserno |
Abstract
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Nature 447(7143): pp. 461-464, 2007.
| How to determine local elastic properties of lipid bilayer membranes
from atomic-force-microscope measurements: A theoretical analysis
Davood Norouzi, Martin Michael Müller, Markus Deserno |
Abstract
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Phys. Rev. E, 74(6): 061914, 2006. See also cond-mat/0602662. Also featured in the Virtual Journal of Biological Physics Research.
| Mechanical Properties of Pore-Spanning Lipid Bilayers Probed by Atomic Force Microscopy
Siegfried Steltenkamp, Martin Michael Müller, Markus Deserno, Christian Hennesthal, Claudia Steinem, Andreas Janshoff |
Abstract
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Biophys. J., 91(1): pp. 217-226, 2006.
| Interface mediated interactions between particles -- a geometrical approach
Martin Michael Müller, Markus Deserno, Jemal Guven |
Particles bound to an interface interact because they deform its shape.
The stresses that result are fully encoded in the geometry and described
by a divergence-free surface stress tensor. This stress tensor can be
used to express the force on a particle as a line integral along any
conveniently chosen closed contour that surrounds the particle. The
resulting expression is exact (i.e., free of any 'smallness' assumptions)
and independent of the chosen surface parametrization. Additional surface
degrees of freedom, such as vector fields describing lipid tilt, are readily
included in this formalism. As an illustration, we derive the exact force
for several important surface Hamiltonians in various symmetric two-particle
configurations in terms of the midplane geometry; its sign is evident in
certain interesting limits. Specializing to the linear regime, where the
shape can be analytically determined, these general expressions yield
force-distance relations, several of which have originally been derived
by using an energy based approach.
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Phys. Rev. E, 72(6): 061407, 2005. See also cond-mat/0506019. Also featured in the Virtual Journal of Biological Physics Research.
| Geometry of surface-mediated interactions
Martin Michael Müller, Markus Deserno, Jemal Guven |
Soft interfaces can mediate interactions between particles bound to
them. The force transmitted through the surface geometry on a
particle may be expressed as a closed line integral of the surface
stress tensor around that particle. This contour may be deformed to
exploit the symmetries present; for two identical particles, one
obtains an exact expression for the force between them in terms of
the local surface geometry of their mid-plane; in the case of a
fluid membrane the sign of the interaction is often evident. The
approach, by construction, is adapted directly to the surface and is
independent of its parameterization. Furthermore, it is applicable
for arbitrarily large deformations; in particular, it remains valid
beyond the linear small-gradient regime.
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Europhys. Lett., 69(3): pp. 482-488, 2005. See also cond-mat/0409043.
2. Books
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New Trends in the Physics and Mechanics of Biological Systems
Lecture Notes of the Les Houches Summer School, vol. 92 (Oxford University Press, 2011),
edited by Martine Ben Amar, Alain Goriely, Martin Michael Müller and Leticia Cugliandolo.
Chapter 9:
The physics of the cell membrane
Martin Michael Müller and Martine Ben Amar.
3. Theses
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Theoretical examinations of interface mediated interactions between colloidal particles,
diploma thesis (2004).
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Theoretical studies of fluid membrane mechanics, dissertation (2007).
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Symmetry breaking in bioelasticity, habilitation thesis (2015).
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